Loans - Summary of TDR and Related Credit Loss Reserves for TDR Loans - Additional Information (Detail) - USD ($)	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other loans included in impaired loans apart from TDR loans	$ 614,000,000	$ 88,000,000
Residential mortgage loan TDR carried at lower of amortized cost or fair value less cost to sell	662,000,000	881,000,000	$ 858,000,000
Non Accrual loans included in TDR loan	610,000,000	676,000,000
Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Additional commitments to lend to commercial borrowers with modified TDRs	205,000,000	$ 112,000,000
Residential Mortgage [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses, loans held for sale	$ 0